Receiver circuit arrangement



Jan. 7, I R. RECHNITZER 2,026,800

RECEIVER CIRCUIT ARRANGEMENT Filed June 28, 1954 INVENTOR PUDOLF AEH/V/fZE/P ATTORNEY Patented Jan. 7, 1936 RECEIVER CIRCUIT ARRANGEMENTRudolf Rechnitzer, Berlin, Germany, assignor to Telefunken Gesellschaftfiir Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation ofGermany Application June 28, 1934, Serial No. 732,751 In Germany May 23,1933 4 Claims. (01. 250-27) In broadcast receivers comprising indirectlyheated-receiver tubes, undesirable actions often occur during what iscalled the incipient stage or period of heating. For instance, in thepresence of fixed regeneration, the receiver during the said period maybe caused to start oscillating as a consequence of the greater slope ormutual conduotance of the tube and, as a result may whistle. It alsohappens rather often that when directly heated power tubes are used thehigh audio frequency amplification during the incipient heating stateoccasions intense bubbling in the loudspeaker which, however, disappearsafter the working process has been completed.

According to the present invention these actions are to be obviated bythat the prematurely active tubes, i. e., the regenerative tube or the,power tube, etc., are impressed during the incipient heating periodautomatically with an abnormally high grid biasing voltage. Thisabnormal biasing voltage may consist of a high positive or negativevoltage according to which one is most suitable in a given case. Thedesired automatic action is to be secured by that the biasing voltage,or part thereof, is obtained in the form of a drop of potential of theapparatus current dependent upon the incipient heating period.

Figure 1 illustrates in circuit diagram form one embodiment of thepresent invention as incorporated in a regeneratively connected circuit,and

Figure 2 shows diagrammatically a preferred embodiment of the inventionin connection with an amplifier circuit provided with indirectly heatedtubes and a filamentary type tube.

Figure 1 shows an exemplified embodiment of the first case where duringthe incipient heating stage a high positive grid biasing potentialprevails, that is, in connection with a regenerative audion. L, C, isthe input circuit which by way of the audion condenser K is associatedwith the control grid of a screen-grid tube. This grid is moreoverconnected by way of the leak resistance RI with the negative terminal ofthe working 'voltage. Regeneration is insured by way'of a circuitcomprising Ll, CI. The plate circuit includes, between anode andpositive source of working voltage, the output resistance R. In parallelrelation to the tube there is connected with the voltage source a seriesarrangement comprising R4, R3, and V. The screen grid is united with apoint between R4 and R3, whence there is established at the same time aconnection, by way of a resistance R2, with the control grid. The latteris here fed with two partial bias voltages. One of these-occasioned byvirtue of the drop of potential across resistance V, at the beginning ofthe heating period, is equal to zero and. thereafter grows gradually. Itcompensates incidentally the positive biasing voltage on thepotentiometer R4, R3, V impressed upon the con- 5 trol grid by way ofthe resistance R2.

Figure 2 shows the case of a directly heated power tube and illustrateshow the high negative biasing potential required according to thisinvention is created. A biasing voltage of the negative sign oifers themerit that overloading of the power tube will be avoided under allcircumstances. At the time of switching in, the biasing potential of thepower tube is given and deter, mined by the fall of potential across thereresistance R, and thus the tube will be blocked. Later on, theincreasing plate currents of the tubes 1 and 2 raise the fall ofpotential across V and thus gradually eliminate the blocking.

I claim:

1. In amplifying apparatus and the like provided with indirectly heatedcathode and directly heated cathode type tubes the latter type beingprovided with at least one grid electrode, and wherein the energizationof all the cathodes is started simultaneously, means for delaying theoperation of a directly heated cathode type tube during the interval oftime taken to heat the cathode of an indirectly heated type tube tosubstantially the normal operating value comprising means for applying abiasing potential to the grid electrode of the directly heated cathodetype tube desired to be controlled which potential is of such value soas to render the tube substantially non-conductive at the beginning ofthe heating period of the cathodes of the tubes and means when thecathode of one of the indirectly heated cathode type tubes is energizedsufliciently to allow normal plate current to flow through the tube forgenerating and impressing a bias potential upon the grid of the directlyheated cathode type tube of such direction and magnitude to render thefirst named bias inefiective and to place a normal operating bias uponthe directly heated cathode type tube.

2. In amplifying apparatus and the like of the type having a pluralityof tubes at least one of which is provided with a cathode which takes anappreciable time to reach its normal operat-- ing temperature and atleast another of which is provided with a cathode which takes less timeto reach its normal operating temperature than the first mentionedcathode and a grid electrode and wherein the energization of all thecathodes of the tubes is started simultaneously, means for delaying theoperation of at least one of the other of said plurality of tubes duringthe interval of time taken to energize the cathode of said firstnamedtube substantially to its normal operating temperature comprising meansfor biasing the grid electrode of said other tube so as to preventoperation thereof from the beginning of the cathode energizing periodand means acting when the cathode of the first named tube reachessubstantially its normal operating temperature and controlled by theflow of current therethrough for automatically changing the efiectivebias on said other tube to render said other tube op erative.

3. In combination, an electric translating circuit including athermionic tube provided with an indirectly heated cathode and athermionic tube provided with a filamentary cathode and a gridelectrode, means for biasing the grid of the second named tube withrespect to its cathode so as to maintain said tube non-conductive afterthe energization of said circuit for a time sufiicient for saidindirectly heated cathode to reach substantially its normal operatingtemperature and means controlled by the flow of current resulting whensaid last named cathode reaches substantially its normal operatingtemperature for changing the effective bias on the second-named tube torender the tube conductive.

4. In combination with an electrical translating circuit including atleast two thermionic tubes and an energizing means therefor, said tubesbeing provided with anode, cathode and grid electrodes, the cathodes ofsaid tubes having different heating characteristics whereby one of thecathodes takes substantially less time to arrive at its normal operatingtemperature than the other thereof, means for biasing the grid of thetube provided with the faster heating cathode so as to maintain saidtube substantially non-conductive after the application of energizingpotentials to said circuit for a time suificient for said slower heatingcathode to reach substantially its normal operating temperature, andmeans controlled by the flow of current resulting when 2 said slowercathode reaches substantially its normal operating temperature forchanging the effective bias on the grid of the faster heating tube torender the tube conductive.

RUDOLF RECHNITZER.

